1. Field of the Invention
The present invention generally relates to devices for managing communication resources, and more particularly, to a communication resource management device for varying the transfer rate of a control channel.
2. Description of the Related Art
A user of a mobile terminal in a mobile communication system can communicate with a desired party by using a communication channel (or information channel) that is set for each call. Setting and management of the communication channel are performed via a control channel. In this case, the data transfer capacity required for the control channel generally differs for each communication system or network. Thus, in terms of effective use of communication resources, it is preferred that allocation of communication resources for the control channel be modified for each communication system.
In regard to this point, Japanese Patent No. 3282708 discloses a technique for improving the efficiency in using communication resources by setting, for each network, an appropriate quantitative ratio on a time axis of the control channel to the information channel. A wireless terminal in this case can establish a connection to any network having a different channel structure by appropriately selecting an operational mode corresponding to each network. However, even within the same mobile communication system, the transfer capacity and/or traffic volume required for the control channel are not always the same. For example, generally, the number of control steps and the transfer quantity of control information are large at the time of connecting a call, but they are reduced during the connection. Thus, conventional techniques such as mentioned above include problems in that it is impossible to flexibly handle such a communication condition.
On the other hand, in a CDMA (Code Division Multiple Access) communication system based on the specification of the 3GPP (3rd Generation Partnership Project), a predetermined transmission band (transfer rate) is assigned for each control channel, and a fixed transfer rate in the control channel is guaranteed in each network. When improving the transfer rate in the control channel related to a certain mobile terminal, a further transmission band is allocated to the mobile terminal without modifying the allocation of transmission band with respect to the control channels of other mobile terminals. Thereby, the data amount that can be transferred within a given length of time is increased in the control channel, and it becomes possible to improve the communication speed. A description of such a condition is given with reference to FIG. 1.
As shown in the left side of FIG. 1, among the available transmission bands in an entire mobile communication system, a part thereof is used for control channels (102), another part thereof is used for a communication channel (104), and the remaining part is empty transmission bands (106). For example, it is assumed that, in order to guarantee a fixed transfer rate with respect to N mobile terminals, a Tw transmission band is allocated to the control channel for each of the mobile terminals, and N×Tw transmission band resources are used for the control channels (102) in the entire system. If two (2×Tw) transmission bands are allocated to a certain mobile terminal in order to improve the transfer rate of the control channel for the mobile terminal, as shown in the right side of FIG. 1, the transmission bands used for the control channels are (N+1)×Tw in the entire system. Since the mobile terminal can use 2×Tw transmission bands, it becomes possible to improve the transfer rate in the control channel.
However, when the transfer rate is improved in the aforementioned manner, since the transmission bands allocated in a fixed manner are increased among the available transmission bands in the entire system, a problem occurs in that the unused bands 106 are reduced. It should be noted that the communication channels 102 include fixed transmission bands necessary for providing various services offered in the mobile communication system, such as an audio channel.
When the unused bands 106 are reduced, first, the number of users that can be further handled in the system is decreased. In addition, since the empty transmission bands vary in accordance with variation in the transmission bands occupied by the control channels, it becomes necessary to perform transmission band management including, for example, monitoring of the empty transmission bands. Consequently, there is a problem in that, for example, management costs in a wireless base station and a radio network controller (RNC) are increased. Further, since it is necessary to, for example, design a system and conduct business investment in consideration of the above-mentioned aspects, there is a problem in that system building is not necessarily easy.